The disclosure relates to an outer casing string and associated method of installation. More particularly, the disclosure relates to a surface casing head that may be run-in through a rotary table and a diverter for installation.
During construction of a wellbore, casing is typically cemented in place to stabilize the wellbore and to prevent the surrounding formation from caving in, and to isolate different regions of the formation. The casing includes a number of individual casing strings installed in a telescoping fashion, including a conductor, an outer casing string, an intermediate casing string, and a production casing string. The outer casing string is installed within the conductor before the wellhead is attached, and supports, at least in part, the remaining casing strings suspended therein. The outer casing string typically includes a surface casing head and an outer casing suspended there from.
A cross-sectional view of a conventional surface casing head is depicted in FIG. 1. As shown, the surface casing head 10 includes a casing head body 15, an inner barrel 20, a lock sleeve 25, an upper packing nut 30, and a lower packing nut 35. The casing head body 15 has a flange 40 at one end that enables coupling of a blowout preventer (BOP) to the surface casing head 10 after installation. Lock sleeve 25 is connected to the inner barrel 20 via a thread with a portion of the casing head body 15 disposed there between. Packing nuts 30, 35 are coupled to the lock sleeve 25 at the upper and lower ends, respectively, of lock sleeve 25. The outer casing, although not shown, is connected to and suspended from the inner barrel 20.
Installation of the surface casing head 10 into the conductor is complex for a number of reasons. Casing head body 15, in particular flange 40, is too large to pass through many conventional rotary tables. Consequently, during installation, the surface casing head 10 must be lowered over the edge of a rig, rather than through a rotary table. This involves moving the surface casing head 10 out of line with the well bore and then repositioning the surface casing head 10 back in line before it can be installed into the conductor. Likewise, flange 40 is too large to pass through many conventional diverters typically installed on the conductor. As a result, the diverter must be removed, surface casing head 10 installed, and the diverter reinstalled. This installation methodology requires multiple trips, and thus is time consuming and costly.
Installation of surface casing head 10 also requires significant manual handling and poses risks to the safety of the individuals involved. After landing an intermediate casing hanger (not shown) within surface casing head 10, packing nuts 30, 35 are manually decoupled from lock sleeve 25. Hydraulic fluid is then injected through a port 45 in lock sleeve 25, causing casing head body 15 to translate axially upward relative to inner barrel 20 to engage the intermediate casing hanger. Once surface casing head 10 is properly landed on the intermediate casing hanger, lock sleeve 25 is manually rotated about inner barrel 20 and moved axially upward to again engage casing head body 15. Movement of lock sleeve 25 in this manner is difficult because the annular space between lock sleeve 25, inner barrel 20, and casing head body 15 is pressurized. After lock sleeve 25 is repositioned in engagement with casing head body 15, packing nuts 30, 35 are manually reinstalled. Movement of lock sleeve 25 about inner barrel 20 to reengage casing head body 15 and subsequent coupling of packing nuts 30, 35 to lock sleeve 25 pose risks to the safety of the individuals involved because surface casing head 10 remains pressurized.
Accordingly, there is a need for a surface casing head and associated method of installation that enables run-in through conventional rotary tables and diverters and requires minimal manual handling, particularly when the surface casing head is pressurized.